Most of today's high brightness liquid crystal display (“LCD”) devices use fluorescent lamp backlights. Although less flexible than light emitting diode (“LED”) backlights, the fluorescent lamp backlights have higher efficiency and, therefore, require less cooling than their LED backlight counterparts.
FIG. 1 illustrates a standard LCD 100 that utilizes LED backlighting. LCD 100 includes a LED backlight panel 102 composed of different colored LEDs 104. Typically, LEDs 104 are arranged in an alternating red, green, and blue pattern. LCD 100 also includes a diffuser 106 situated between backlight panel 102 and LCD panel 108.
LED backlight panel 102 creates a light source 110 with a relatively structured intensity, ILED (x,y). Diffuser 106 transforms light source 110 emitted from LED backlight panel into light source 112 with a substantially uniform intensity, I0. Diffuser 106 allows both light and dark areas of a video to be equally illuminated on the backside of LCD panel 108. To create viewable video, LCD panel 108 changes the transmittance of each individual LCD pixel in LCD panel 108 based on an input signal to produce a video 114 with a varied intensity, ILED (x,y). Accordingly, the intensity of the video intensity ILCD (t,x,y) seen by a user of LCD 100 at a certain time corresponds to the desired video.
In LCD 100 that includes LED backlight panel 102, diffuser 106 and LCD panel 108, the desired video's intensity would be governed by the equation:ILCD(t, x, y)=I0T0LCD(t, x, y)
Where:
ILCD(t,x,y) is the intensity of the video signal at a time t,
I0 is the uniform intensity from diffuser 106, and
T0LCD(t,x,y) is the transmittance of LCD panel 108 at time t.
In most video displayed on an LCD whether text, still images, or moving pictures, the different parts of the screen will have vastly different intensity levels depending on the video. Thus, in order to produce the different intensity levels, the LED backlight produces a high intensity light source to match the brightest portion of the video. Then, the intensity of the light source is reduced by changing the transmittance of the LCD panel for portions of the video that require a less intense illumination. Accordingly, the LED backlight must be supplied with high power constantly in order to produce the high intensity output to match the brightest portion of the video.
For example, if LCD 100 is displaying a video of a sunrise, LED backlight 102 would produce a uniform light source for the brightest portion of the video, i.e. the sun. Then, to create darker portions of the video, the transmittance of LCD panel 108 at locations other than the sun would be reduced. According to this method, the backlight must be powered at the intensity of the brightest portion of the video, even if the brightest portion makes up only a small amount of the entire video.